This invention relates to a flame-retardant composition and to a resinous composition containing same. More particularly, this invention relates to a crude phosphate ester flame retardant composition of reduced acidity and to a hydrolysis-susceptible resin containing the aforesaid flame retardant composition.
Phosphate esters are widely used as halogen-free, flame retardants for addition to engineering plastics, e.g., polyphenylene oxide/high-impact polystyrene and poplycarbonate/acrylonitrile-butadiene-styrene blends. A disadvantage associated with phosphate esters such as resorcinol bis(diphenyl phosphate) and bisphenol A bis(diphenyl phosphate) is the difficulty of preparing them in a purity meeting the stringent requirements of the polymer industry.
In the preparation of phenylphosphate esters starting either from phosphorus oxychloride, an aromatic diol and phenol or a phenylchlorophosphate and an aromatic diol, the presence of any moisture in the starting materials may result in an increase in the acidity of the final product which will cause hydrolytic instability in hydrolysis-susceptible resins and blends of such resins when incorporated therein. In general, in order to reduce the content of acidic impurities in phenylphosphate esters, neutralization with an alkaline metal hydroxide or other basis compound such as magnesium hydroxide is carried out, followed by multiple water washes and distillation to obtain the pure phenylphosphate esters. Formation of undesirable emulsions with the phenylphosphate esters may accompany such methods.
U.S. Pat. No. 5,616,768 discloses an involved multi-step process for producing phenylphosphate esters of low acidity wherein a crude phenylphosphate ester product is treated with an epoxy compound and the resultant material is heated in the presence of water, washed with water, the residual water removed by distillation. This process is capital intensive and uneconomical to carry out.
It is an object of the present invention to provide a phosphate ester flame retardant composition of low acidity which can be simply and economically produced.
It is a further object of the invention to provide such a flame retardant composition for resins that are susceptible to hydrolysis and a consequent degradation of their useful properties, in particular, for polycarbonates, polyesters and their blends.
It is a further particular object of the invention to provide a hydrolytically stable blend of polycarbonate and a styrene-based resin such as acrylonitrile-butadiene-styrene (ABS) copolymer containing as a flame retardant component thereof a phosphate ester of low acidity.